To apply an AutoCorrect rule, enter the predefined text in the document and press the Spacebar.
To turn off AutoCorrect in LibreOffice Writer choose Tools - AutoCorrect - While Typing. Refer to the help page Turning Off AutoCorrect to learn more about deactivating AutoCorrect in LibreOffice Writer.
To apply AutoCorrect to an entire text document, choose Tools - AutoCorrect - Apply.
To turn off AutoCorrect in LibreOffice Calc, go to Tools - AutoCorrect Options and uncheck all items in the Options and Localized Options tabs. Refer to the help page Turning Off AutoCorrect to learn more about deactivating AutoCorrect in LibreOffice Calc.